The present invention relates primarily to magnetic write and read of data and can be used in arrangements with reverse digital high-density memory devices which are intended for operations with large data arrays and in other electronic equipment.
One of the fundamental units in the modem computer technology and in other electronic systems is a memory device, the efficiency of which is characterized by the following basic parameters: stored data capacity and write density, access time (duration of the whole cycle of random address data retrieval), non-volatility of storage (possibility to store data in the event of power loss), lifetime under use and cost for mass production of 1 MB of the memory.
Recently, optical disks surpassed all other memory devices in capacity (from 128 to 2000 MB), but unfortunately, they are either not adapted to the rewrite operations or their write and read time is very long (for example, the access time amounts to 30-50 ms). The hard magnetic disks can store large arrays of information (up to 10 GB) and possess a rewrite capability. The access time is reduced to 8-15 ms, and yet it is still very long. Both types of memory devices (optical disks and hard magnetic disks) are non-volatile.
A dynamic random-access memory (DRAM) employs a charged capacitor as the data storing element (memory cell). Such devices are made in a form of integrated circuits, which results in a very short access time of about 10-50 ns and a write density of 3-12 MB/cm.sup.2 . However, DRAMs are volatile and require a periodic refreshing.
A static memory device employs a solid-state gate in the transistor assembly storing element (memory cell). Such devices are intricate for fabrication and can be used only as a cache memory, i.e., as a buffer for exchange between the slow and fast memory devices. The disadvantages of static memories are limited non-volatility, comparatively low density (1-2 MB/cm.sup.2) and rather high cost.
Recently, efforts have been made to create a memory device that is free of the above disadvantages, but concurrently provides a high density of writing (about 100 MB/cm.sup.2), a short access time (about 10 ns), is non-volatile has an unlimited number of rewrite and read cycles, and a low cost of fabrication. The so-called ferroelectric and magnetic memory devices meet these requirements most closely.
It is known that a numerous class of polycrystals, designated as ferroelectrics, possesses the property of being able to maintain the state of a given electrical polarization for a long time. This property allows them to be used in memory cells instead of the dielectric between the capacitor plates in the dynamic memory with the result that the dynamic memory takes on the property of nonvolatility.
Unfortunately, the ferroelectric memory devices have a limited lifetime. Even after a limited number of polarization reversals, the ferroelectric begins to age due to accumulating a spurious electric charge in the crystal. The absolute magnitude of the electrical polarization in the memory cell decreases, and the cell becomes less operable and eventually loses its memory properties (U.S. Pat. No. 5,768,182, Int.Cl. H01L 31/062 (365/145), 1998).
The same disadvantage is peculiar to the memory devices based on other high-quality dielectrics, as the mere fact of availability of electric charges inevitably leads to gradual ageing of the dielectric memory through the leakage of the spurious charge (U.S. Pat. No. 5,796,670, Int. Cl. G11C 13/00 (365-228), 1998).
There is a method and a device with a so-called "magnetic" random access memory (MRAM), where the write and read operations rest on the property of a conductor to change the electrical resistance in the event of applying a magnetic field (effect of anisotropic resistance (AMR) or giant magnetoresistance (GMR)).
The device comprises either individual circuits for writing and reading data or (in the event of using conductors with the GMR) multilayer structures. Each memory cell comprises separate elements for writing, storing and reading the data. Such a memory cell is capable of bearing a practically unlimited number of rewriting cycles, due to stability of the so-called "exchanging" forces of interactivity of atomic electrons and by the absence in the nature of magnetic charges that could lead to depolarization of the magnetic dipole moments of data carriers (U.S. Pat. No. 5,587,943, Int.Cl. G11C 11/15 (365/158, 1996).
A disadvantage of this method is that the effect of the AMR manifests itself only against the background of very high ohmic resistance of conductors. When a single circuit is used both for writing and for reading the information, a strong current is passed through the conductor, this results in manifestation of an electromigration effect (transfer of a portion of the substance of the current busbar together with the electrical current), which leads to the loss of normal operation of the memory cell.
Additional disadvantages of a device realizing the method are rather low write density and difficulty of its fabrication, while the usage of conductors with the GMR results in strong dependence of the device operation on the temperature, i.e., lower temperatures are preferable.
A memory device (magnetic transistor) is known, whose operation is based on using spin dependent effects of transferring the charges in a magnetic field (electron tunneling effect). The charge tunneling in the magnetic transistor between two layers of a metal ferromagnetic, separated by a layer of the dielectric, is controlled by the magnetic field (U.S. Pat. No. 5,650,958, Int. Cl. G11B 5/127 (365/173), 1997).
A disadvantage of this design is the dependence of the memory device operation on the temperature, i.e., the warm-up of the device during long-term operations causes instability of hysteresis curves. In addition, the technology of the device fabrication is complicated; it is required to apply about ten layers of various materials, including dielectrics. There is a method and a memory device to realize it, which is based on usage of magnetic particles (domains) being longitudinally or transversely arranged on the carrier and possessing magnetic dipole moments.
For writing and reading the information the memory device uses relative movement of a carrier with magnetic particles and a magnetic head, which generates during writing and records during reading a magnetic field which is homogeneous in direction and varying in strength. The writing density in this case is at the level of 10.sup.8 -10.sup.9 bit/cm.sup.2 (M. B.Gitlits "Magnetic Recording of Signals", Moscow, "Radio & Svyaz", 1990, p.232).
Among the disadvantages of the above design are limitations of the writing density resulting from the rigid coupling of magnetic particles (domains) during multiplexing, a risk of losing information under influence of external fields, as well as a limited lifetime of carriers and a limited reliability of memory devices due to the necessity to use units which execute high speed mechanical motion for write and read operations.
There is a method of magnetic-toroid writing and reading of information based on the interaction of magnetized particles of the carrier, which are concentrically closed into toroid-like patterns (aggregates of the carrier's magnetic particles) with a controlling vortex magnetic field: The magnetic field changes the orientation of the moments of magnetic particles during writing of information and registers the parameters of electrical field excited by moving aggregates of the carrier's magnetic particles during reading of information (V. M. Dubovik, A. M. Martsenyuk, N. M. Martsenyuk "Magnetic reversal of Aggregates of Magnetic Particles by a Vortex Magnetic Field and Usage of a Toroid Feature for Data Writing." Reprint of Joint Institute for Nuclear Research, R .17-92-541, 1992). Two magnetization states of such aggregates, referred to as logical "0" and logical "1" in the digital code, differ by opposite (clockwise or counter-clockwise) directions of the magnetization vortex and, accordingly by oppositely oriented vectors of toroid moments.
The package density of particle aggregates with toroid magnetization is practically limited only by their sizes by virtue of weak interaction between aggregates. The nano-technology methods allow one to obtain single-domain ferromagnetic particles of size 1-10 nm with a saturation magnetization in the order of 300 emu/cc. For example, an aggregate consisting of four such particles has a toroid magnetization with the strength of the vortex magnetic field between the aggregate's particles of about 10.sup.3 oersted. This is sufficient for the aggregate stability and hence for reliable long-term storage of information. Since each of those aggregates is capable of storing 1 bit of information and the area of the aggregate is 10-100 nm.sup.2, the writing density will be equal to 10.sup.12 -10.sup.13 bit/cm.sup.2.
A disadvantage of this design is the complexity of its implementation. During reading of a separate data bit, it requires difficult-to-attain quick travel of the reading unit relative to the carrier of stored information and, during writing, requires a difficult-to-get toroid moment value needed for providing the vortex magnetization reversal of an aggregate with the alternative electric field.
Besides, the application of a flat capacitor for creating a vortex magnetic field does not allow a high degree of localization of the vortex field within the limits of one aggregate having a nanometric size.
A prior art method of toroid data writing and reading which is close to the invention consists in that toroid-like patterns are formed in a material, for example magnetic, each of these patterns has a closed magnetic flux with an appropriate direction of twisting; during writing a unit of alternative information, the twisting direction of the closed magnetic flux in respective toroid-like patterns is changed (Russian Federation (RF) Pat. No. 2114466, Int.Cl. G11B 5/00, 5/852, 1998). However, the known method does not provide a random access to the memory, has a rather long access time, and requires a complex process of phase detection during reading operations, especially at high frequencies.
A prior art memory cell which is close to the invention incorporates a toroid-like element made of a magnetic material and placed in an insulating medium (Russian Federation Pat. No. 2114466, Int.Cl. G11B 5/00, 5/582, 1998). Unfortunately, the known device is unable to provide the required writing density and speed and is complicated in manufacturing.
A prior art memory device which is close to the invention, realizing the above mentioned method of data writing and reading, comprises toroid-like elements, a means for magnetic reversal of toroid-like elements and an electronic control unit (Russian Federation Pat. No. 2114466, Int.Cl. G11B 5/00, 5/852, 1998). However, the known device is unable to provide the required writing density and speed and is complicated in manufacturing.
Besides, the write and read head is a matrix with numerous nanometrical needles, fixed in the dielectric, and requires a precision device, which shall provide relative travel of the head and of the carrier of toroid-like magnetic patterns.